S1 ←S0 vibronic spectrum and the structure of the chloral molecule in theS1 stateS0 vibronic spectrum and the structure of the chloral molecule in theS1 state

The vibronic absorption spectrum of chloral (CCl3COH) vapors is studied in the region of S1 ← S0 electron transition (32,000–28,700 cm−1). The 29,070 cm−1 vibronic transition (not observed because of low intensity) is believed to be the ‘start’ of the electron transition. Several fundamentals are found in the S0 and S1 states. Inversion splitting of the zero vibrational level in the S1 state of chloral, indicating a nonplanar structure of the carbonyl fragment, is found. The intensity ratio of the torsional transition bands indicates that the S1 ← S0 electronic excitation of the chloral molecule causes significant changes in the orientation of the −CCl3 group relative to the molecular framework. The potential functions of internal rotation (S0 and S1 states) and inversion (S1 state) of the chloral molecule are determined from experimental data. The potential barriers of internal rotation (S0 and S1 states) and inversion (S1 state) are 380, 780, and 760 cm−1 (4.5, 9.3, and 9.1 kJ/mole), respectively.